Injection Molding

Injection molding is a process used to form
products from plastic. The processrequires a mold, clamping component,
injection unit, and some sort of plastic.

As time has advanced so has
injection molding by developing new techniques andnew products to aid in the
manufacturing of the injection molded parts.

Injection molding was used
as early as the 1860ís. It can be used to form manydifferent products.
Whether the products are small, large, complex, or simplethey can be
produced. Injection molding has derived from metal die casting.

However,
the polymer canít just be poured into a mold, it has to be forcedinto the
mold cavity. The polymer is forced into the mold and pressure is heldon it
to avoid shrinkage in the mold cavity as it cools. Injection molding
iscapable of producing a large number of parts with very high precision.
Allthermoplastics except polytetraflouroethylene (PTFE), polyamides, and
somearomatic polyesters can be used by the injection molding machine.
Somethermosetting plastics can also be used. The typical fabrication process
can bedone by one of two different types of injection molding equipment.
Either aplunger, or reciprocating screw type machine can be used. The
process starts bymelting the polymer resin. Once the resin is melted, a mold
is placed in theclamping unit. The clamping unit is to hold the mold
together. The plunger orreciprocating screw then force the polymer resin
into the mold. In the plungeroperated machine, the plunger is hydraulically
operated. This forces the plasticthrough a heated area, where it is then
spread into a thin layer by the torpedo.

Then the melt comes to the
nozzle and is injected into the mold. Thereciprocating screw rotates, this
moves the polymer resin forward for injection.

As the screw rotates it
acts to melt, mix, and pump the polymer to prepare itfor injection. The
reciprocating screw machine is the most widely used of thetwo machines. Once
the polymer resin is injected into the mold cavity, the moldis allowed to
cool. The mold has a gate, which limits back flow and directs theflow of the
melt into the mold cavity. Once the mold has cooled and the polymerhas
solidified the mold can be removed and the part can be ejected. When thegate
freezes, the screw begins to rotate again and the part is ejected.
Thiscompletes the cycle time. Cycle times range due to the amount of time
thepolymer needs to cure or solidify. This is called the hold time. Some
advantagesof injection molding are high production rates, design
flexibility, lowtolerances, can process wide range of materials, low labor,
little or nofinishing, and scrap is held to a minimum. However, some
disadvantages are highstartup and running costs, part must be designed for
effective molding, accuratecost prediction is difficult, and machine cost is
very high. The high toolingcosts come from the molds being built to a high
level of precision. The moldsare usually constructed of hardened tool steel,
and aluminum or other softmetals when tooling life is not an issue. Tooling
costs can range from $5,000 to$100,000. However, there are some parts that
can not be formed by any othermethod of processing except injection molding.
These parts typically becomefeasible around 1,000 pieces. To go with the
high tooling costs there are alarge number of variables that go along with
it. Injection molding machines mayrequire special plant services that other
equipment does not. As technologyadvances so must the industry to keep up
production. One way injection moldingis keeping up is by becoming automated.
Usually, operators are placing partsinto molds, and then taking the parts
out. Now, robotic devices are being usedto place inserts before molding and
remove parts after molding as well as a hostof other operations as well. Not
only does the robotics speed up the process,but makes it much more cost
effective. Another way industry is trying to keep upwith technology is by
using computer software. The software is called "Mold

Adviser," which is
a mold design and analysis package that can be used to helpspeed up
operations while reducing tooling costs. Using the past standardoperation of
designing molds a company could easily waste six to twelve weeksand anywhere
from $30,000 to $40,000 on fixing a mold that has a problem withfilling
correctly. The new software will detect these problems up front
beforeproduction begins. It is used with a CAD program, and is really
divided into twoparts. The Part Advisor and the Mold Advisor. The Part
Advisor can test theparts design and analyze the part to see if it will fill
correctly. Once thepart has been analyzed, users begin the Mold Advisor. The
Mold Advisor will helpsetup gates and runner systems, predict plastic flow,
shot size, and cycle time.

Users of the new software have reported that
the software is easily learned anduser friendly. Injection molded products
include TV, VCR, CDís, CD players andcomputer housings. So, one can see the
impact that the products of injectionmolding have on our every day life.
Injection molding has been used since the

1860ís. Products of all sizes
and shape have been produced. However, withadvancing technology and the high
cost of molds it will be interesting to seehow much further injection
molding will advance and how it will advance in
thefuture.